The present invention relates to a holding apparatus that holds an optical element, and an exposure apparatus.
For a position measuring part in an optical element holding unit that includes a driving part that drives an optical element, and a position measuring part that measures a position of the optical element, the conventional technology uses two types of position adjustment apparatuses (see, for example, Japanese Patent Laid-Open No. (“JP”) 2003-337272).
A holding unit shown in FIG. 13 of JP 2003-337272 provides a position adjusting mechanism with two degrees of freedom which can drive an object in a center axis direction and a tangential direction, at three locations along the circumferential direction. An optical element has six driving degrees of freedom in a XYZ orthogonal coordinate system having a Z-axis as an optical axis of the optical element, and a XY plane perpendicular to the Z axis. The optical element is allowed to translate in each of the X-axis direction, Y-axis direction, and Z-axis direction, to tilt around each of the X axis and the Y axis, and rotate around the Z axis.
The holding unit has a position measuring part that measures a position of the optical element, and is provided at three locations along the circumferential direction. The position measuring part uses a biaxial electrical capacitance sensor that detects a displacement between an optical axis direction and outer-circumferential tangential direction of the optical element.
The holding unit shown in FIG. 2 of JP 2003-337273 includes a position adjusting mechanism that drives an optical element in the optical axis direction using a piezoelectric actuator and is provided at three locations along the circumferential direction, allowing the optical element to translate in the Z-axis direction and to tilt around each of the X axis and the Y axis.
The position measuring part of the optical element is provided at three locations around the circumferential direction. The position measuring part is an optical linear encoder that detects a displacement of the optical element in the optical axis direction.
The holding unit shown in FIG. 13 of JP 2003-337272 uses the electrical capacitance sensor for the position measuring part, and is inferior to an interference type displacement gage in detection resolution, dynamic range, and linearity of the detection output signal. The electrical capacitance sensor can detect an absolute position.
In addition, the holding unit shown in FIG. 2 of JP 2003-337272 uses an optical linear encoder that detects a displacement of an optical element in the optical axis direction, and thus can detect only a relative moving amount of a target, resulting in an incapable cognition of an absolute position of the optical element when holding unit is restarted after the power is shut down. Thus, the optical element cannot be reset to a coordinate value before the power is shut down.
The holding unit shown in FIG. 2 and that shown in FIG. 13 in JP 2003-337272 hold separate optical elements.